﻿//-----------------------------------------------------------------------
// <copyright file="TaskExtensions.cs" company="The Outercurve Foundation">
//    Copyright (c) 2011, The Outercurve Foundation. 
//
//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
//      http://www.apache.org/licenses/LICENSE-2.0
//
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.
// </copyright>
// <author>Nathan Totten (ntotten.com), Jim Zimmerman (jimzimmerman.com) and Prabir Shrestha (prabir.me)</author>
// <website>https://github.com/facebook-csharp-sdk/facbook-csharp-sdk</website>
//-----------------------------------------------------------------------

namespace Facebook
{
    using System;
    using System.Threading.Tasks;

    static class TaskExtensions
    {
        public static Task<T2> Then<T1, T2>(this Task<T1> first, Func<T1, T2> next)
        {
            if (first == null) throw new ArgumentNullException("first");
            if (next == null) throw new ArgumentNullException("next");

            var tcs = new TaskCompletionSource<T2>();
            first.ContinueWith(delegate
            {
                if (first.IsFaulted) tcs.TrySetException(first.Exception.InnerExceptions);
                else if (first.IsCanceled) tcs.TrySetCanceled();
                else
                {
                    try
                    {
                        var result = next(first.Result);
                        tcs.TrySetResult(result);
                    }
                    catch (Exception ex)
                    {
                        tcs.TrySetException(ex);
                    }
                }
            });
            return tcs.Task;
        }
    }
}